<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>div圆周运动</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }

        .box {
            width: 200px;
            height: 200px;
            border: 1px solid blue;
            border-radius: 100%;
            border-top: 0px;
            margin: 30px auto 0;
            position: relative;
        }

        .pointer {
            left: 0;
            top: 0;
            position: absolute;
            width: 10px;
            height: 10px;
            background-color: rebeccapurple;
            z-index: 100;
        }
    </style>
</head>

<body>
    <div class="box">
        <div class="pointer" id="pointer"></div>
    </div>
    <script>
        let div = document.querySelector('#pointer');
        let R = 100; //半径
        let angle = 0; //开始角度
        const maxAngle = 180;
        function animation() {
            //角度转弧度
            var radians = angle * (Math.PI / 180);
            div.style.left = R * Math.cos(radians) + 100 + 'px';
            div.style.top = R * Math.sin(radians) + 100 + 'px';
            if (angle >= maxAngle) {
                angle = 0;
            }
            else {
                angle = angle + 1;
            }
            requestAnimationFrame(animation);
        }
        animation();
    </script>
</body>

</html>